1. FIELD OF THE INVENTION
This invention relates to systems for processing signals and, more particularly, to systems for digitally filtering undesired signals and for sensing physical parameters.
2. PRIOR ART
In certain applications signals are produced which may vary over a range of a million to one, requiring signal resolutions of one part per million. For example, certain inertial navigation systems require such accuracy. For achieving a dynamic range of a million to one, a conventional parallel analog-to-digital conversion circuit requiring 20 bits per sample would be extremely difficult to fabricate and keep in calibration with aging of components and over a range of temperatures. For these applications, a voltage-to-frequency converter is normally used which generates an output signal having a frequency proportional to the voltage level of an input baseband signal. By counting the frequency of the signal produced by the voltage-to-frequency converter over a finite time interval, a quantity representing the integral of the input baseband signal can be computed. The input baseband signals to be measured in such systems have a frequency range which extends down to dc. Shifts in dc level in the circuits of a system are caused, for example, by temperature changes or by subjection to external radiation. Consequently, any shifts in the dc level within any circuit handling a baseband signal limits the voltage accuracy of a system.